Localization of Spiropyran Activation.

Functionalization of planar and curved glass surfaces with spiropyran (SP) molecules and localized UV-induced activation of the mechanophore are demonstrated. Fluorescence spectra of UV-irradiated SP-functionalized surfaces reveal that increases in surface roughness or curvature produce more efficient conversion of the mechanophore to the open merocyanine (MC) form. Further, force-induced activation of the mechanophore is achieved at curved glass-polymer interfaces and not planar interfaces.

Rapid Degradation of Poly(lactic acid) with Organometallic Catalysts.

Poly(lactic acid) (PLA) is an effective sacrificial material for the creation of vascular networks in thermoset polymers and composites. The high thermal stability of PLA limits its applications as an embedded sacrificial template in high-temperature-resistant thermoset matrices. Here, we demonstrate faster and more efficient PLA degradation at temperatures lower than previously reported using two organometallic catalysts: tin(II) oxalate (Sn(Oxa)) and tin(II) acetate (Sn(Ac)).

Self-Protecting Epoxy Coatings with Anticorrosion Microcapsules.

The corrosion of steel substrates causes damage that is costly to repair or replace. Current protective coatings predominately rely on environmentally harmful anticorrosive agents and toxic solvents to protect the underlying substrate. The use of lawsone (2-hydroxy-1,4-napthoquinone) together with a water-based epoxy coating provides an environmentally friendly alternative for common protective coatings.

Enhanced Mixing of Microvascular Self-Healing Reagents Using Segmented Gas-Liquid Flow.

Microvascular self-healing systems have previously been demonstrated to restore large-scale damage and achieve repeated healing of multiple damage events in polymers. However, the healing performance of these systems is often limited because the laminar nature of flow in microchannels  results in poor mixing of two-part self-healing reagents. In this paper, we introduce segmented gas-liquid flow (SGLF) to enhance the mixing of reagents in microvascular self-healing systems.

Core-Shell Microcapsules Containing Flame Retardant Tris(2-chloroethyl phosphate) for Lithium-Ion Battery Applications.

Flame retardant tris(2-chloroethyl phosphate) (TCP) is successfully encapsulated in core-shell poly(urea-formaldehyde) microcapsules by in situ polymerization. The microcapsules are electrochemically stable in lithium-ion (Li-ion) battery electrolytes and thermally stable to ca. 200 °C.

Rapid energy-efficient manufacturing of polymers and composites via frontal polymerization.

Thermoset polymers and composite materials are integral to today's aerospace, automotive, marine and energy industries and will be vital to the next generation of lightweight, energy-efficient structures in these enterprises, owing to their excellent specific stiffness and strength, thermal stability and chemical resistance. The manufacture of high-performance thermoset components requires the monomer to be cured at high temperatures (around 180 °C) for several hours, under a combined external pressure and internal vacuum . Curing is generally accomplished using large autoclaves or ovens that scale in size with the component.

Accelerated Thermal Depolymerization of Cyclic Polyphthalaldehyde with a Polymeric Thermoacid Generator.

Thermally triggerable polymer films that degrade at modest temperatures (≈85 °C) are created from a blend of cyclic polyphthalaldehyde (cPPA) and a polymeric thermoacid generator, poly(vinyl tert-butyl carbonate sulfone) (PVtBCS). PVtBCS depolymerizes when heated, generating acid which initiates the depolymerization of cPPA into volatile byproducts. The mass loss onset for 2 wt% PVtBCS/cPPA is 22 °C lower than the onset for neat cPPA alone in dynamic thermogravimetric analysis experiments.

Interfacial Mechanophore Activation Using Laser-Induced Stress Waves.

A new methodology is developed to activate and characterize mechanochemical transformations at a solid interface. Maleimide-anthracene mechanophores covalently anchored at a fused silica-polymer interface are activated using laser-induced stress waves. Spallation-induced mechanophore activation is observed above a threshold activation stress of 149 MPa.

Cyclic Poly(phthalaldehyde): Thermoforming a Bulk Transient Material.

Cyclic poly(phthalaldehyde) (cPPA) is a metastable and stimuli responsive polymer that undergoes rapid solid state depolymerization and has been utilized as a packaging and encapsulating material for transient applications. However, the early onset thermal depolymerization of cPPA severely hinders the fabrication and processing of plastic parts. Herein, the thermally triggered depolymerization of cPPA was investigated and tailored to enable thermal processing and molding of cPPA at moderate temperatures below the thermal depolymerization temperature.

Time Release of Encapsulated Additives for Enhanced Performance of Lithium-Ion Batteries.

Time release of encapsulated vinylene carbonate (VC) from microcapsules in Li-ion batteries is demonstrated to enhance the rate performance without sacrificing capacity retention. VC-filled microcapsules are successfully prepared by the solvent exchange method that allows VC to diffuse through the microcapsule shell wall at an elevated temperature. The concentration of VC added directly to the electrolyte in a pouch cell (2 wt %) significantly decreases after the first cycle at C/10-rate.

Alkyl Phosphite Inhibitors for Frontal Ring-Opening Metathesis Polymerization Greatly Increase Pot Life.

Frontal ring-opening metathesis polymerization (FROMP) has potential for use in rapid fabrication of structural polymers. However, the high activity of the ruthenium catalyst used for FROMP has limited the working time to <1 h. We report the use of alkyl phosphites as inhibitors for Grubbs' type catalysts to substantially extend working time.

Low-Ceiling-Temperature Polymer Microcapsules with Hydrophobic Payloads via Rapid Emulsion-Solvent Evaporation.

We report a microencapsulation procedure based on rapid solvent evaporation to prepare microcapsules with hydrophobic core materials and low-ceiling-temperature polymer shell wall of cyclic poly(phthalaldehyde) (cPPA). We use and compare microfluidic and bulk emulsions. In both methods, rapid solvent evaporation following emulsification resulted in kinetically trapped core-shell microcapsules, whereas slow evaporation resulted in acorn morphology.

Encapsulation of grape seed extract in polylactide microcapsules for sustained bioactivity and time-dependent release in dental material applications.

Objective: To sustain the bioactivity of proanthocyanidins-rich plant-derived extracts via encapsulation within biodegradable polymer microcapsules.

Methods: Polylactide microcapsules containing grape seed extract (GSE) were manufactured using a combination of double emulsion and solvent evaporation techniques. Microcapsule morphology, size distribution, and cross-section were examined via scanning electron microscopy.

Effect of Mechanical Stress on Spiropyran-Merocyanine Reaction Kinetics in a Thermoplastic Polymer.

Mechanical force alters the potential energy surface of a mechanophore reaction by modifying the activation energy for conversion. The effects of force on the rate constants and activation energies are not well characterized for mechanophores in bulk polymers. In this work, spiropyran-linked polyurethanes are synthesized and the kinetics of the spiropyran-merocyanine transition in the bulk polymer measured under different values of a macroscopic tensile stress.

Polymers with autonomous life-cycle control.

The lifetime of man-made materials is controlled largely by the wear and tear of everyday use, environmental stress and unexpected damage, which ultimately lead to failure and disposal. Smart materials that mimic the ability of living systems to autonomously protect, report, heal and even regenerate in response to damage could increase the lifetime, safety and sustainability of many manufactured items. There are several approaches to achieving these functions using polymer-based materials, but making them work in highly variable, real-world situations is proving challenging.

A Robust Damage-Reporting Strategy for Polymeric Materials Enabled by Aggregation-Induced Emission.

Microscopic damage inevitably leads to failure in polymers and composite materials, but it is difficult to detect without the aid of specialized equipment. The ability to enhance the detection of small-scale damage prior to catastrophic material failure is important for improving the safety and reliability of critical engineering components, while simultaneously reducing life cycle costs associated with regular maintenance and inspection. Here, we demonstrate a simple, robust, and sensitive fluorescence-based approach for autonomous detection of damage in polymeric materials and composites enabled by aggregation-induced emission (AIE).

Regioisomer-Specific Mechanochromism of Naphthopyran in Polymeric Materials.

Transformation of naphthopyran into a colored merocyanine species in polymeric materials is achieved using mechanical force. We demonstrate that the mechanochemical reactivity of naphthopyran is critically dependent on the regiochemistry, with only one particular substitution pattern leading to successful mechanochemical activation. Two alternative regioisomers with different polymer attachment points are demonstrated to be mechanochemically inactive.

Malleable and Recyclable Poly(urea-urethane) Thermosets bearing Hindered Urea Bonds.

Poly(urea-urethane) thermosets containing the 1-tert-butylethylurea (TBEU) structure feature a reversible dissociation/association process of their covalent linkages under mild conditions. Unlike conventional thermosets, TBEU-based poly(urea-urethane) thermosets maintain their malleability after curing. Under high temperature (100 °C) and applied pressure (300 kPa), ground TBEU thermoset powder can be remolded to bulk after 20 min.

Autonomous Indication of Mechanical Damage in Polymeric Coatings.

High-resolution in situ autonomous visual indication of mechanical damage is achieved through a microcapsule-based polymeric material system. Upon mechanical damage, ruptured microcapsules release a liquid indicator molecule. A sharp color change from light yellow to bright red is triggered when the liberated indicator 2',7'-dichlorofluorescein reacts with the polymeric coating matrix.

Biomimetic Self-Healing.

Self-healing is a natural process common to all living organisms which provides increased longevity and the ability to adapt to changes in the environment. Inspired by this fitness-enhancing functionality, which was tuned by billions of years of evolution, scientists and engineers have been incorporating self-healing capabilities into synthetic materials. By mimicking mechanically triggered chemistry as well as the storage and delivery of liquid reagents, new materials have been developed with extended longevity that are capable of restoring mechanical integrity and additional functions after being damaged.

Thermally triggered degradation of transient electronic devices.

Thermally triggered transient electronics using wax-encapsulated acid, which enable rapid device destruction via acidic degradation of the metal electronic components are reported. Using a cyclic poly(phthalaldehyde) (cPPA) substrate affords a more rapid destruction of the device due to acidic depolymerization of cPPA.

Core-shell polymeric microcapsules with superior thermal and solvent stability.

A protective polydopamine (PDA) coating is applied to core-shell microcapsule surfaces by the polymerization of dopamine monomers. A neutral aqueous solution and the addition of an oxidant (i.e.

Triggered transience of metastable poly(phthalaldehyde) for transient electronics.

Triggerable transient electronics are demonstrated with the use of a metastable poly(phthalaldehyde) polymer substrate and encapsulant. The rate of degradation is controlled by the concentration of the photo-acid generator and UV irradiance. This work expands on the materials that can be used for transient electronics by demonstrating transience in response to a preselected trigger without the need for solution-based degradation.

Rapid stiffening of a microfluidic endoskeleton via frontal polymerization.

Materials capable of rapidly modifying their physical properties in response to stimuli are desirable for on-demand deployment and adaptive engineering structures. Frontal polymerization is a self-propagating reaction that can quickly transform liquid reactants into solid products. In this contribution, we demonstrate that frontal polymerization enables facile, rapid stiffening of a vascular network embedded in a flexible matrix.